The objective of this project is to elucidate the neuroanatomy of neurotransmitter-phosphoprotein interactions in part of the extended amygdala of the rat, which is composed of the nucleus accumbens, the lateral subdivision of the bed nucleus of the stria terminalis, the olfactory tubercle, the sublenticular substantia inominata, and the central nucleus of the amygdala. The main structures to be investigated are the nucleus accumbens, bed nucleus of the stria terminalis, and central nucleus of the amygdala. These nuclei have a number of properties in common, including afferent and efferent connectivity, neuropeptide and neurotransmitter content, and their putative involvement in a variety of neuropsychiatric disorders, including schizophrenia. The neuroanatomical studies described herein will involve the use of immunocytochemical and in situ hybridization methodologies to investigate four phosphoproteins enriched in the extended amygdala. These are the dopamine- and cAMP-regulated phosphoprotein DARPP-32, the vasoactive intestinal polypeptide-and cAMP regulated phosphoproteins ARPP-21 and ARPP- 16, and phosphatase inhibitor-1, a protein which is closely related to DARPP-32. Immunocytochemistry will be used for regional and subcellular distribution studies of these phosphoproteins. This technique will also be used to study the overlap between phosphoprotein-containing neurons, and nerve terminal populations containing dopamine, vasoactive intestinal polypeptide, and calcitonin gene-related peptide, each of which has been demonstrated to have an effect on protein phosphorylation. Double-labeling immunocytochemistry will be performed at the electron microscopic level to determine the ultrastructural relations between these chemically identifiable neural elements. The major sources of immunoreactive afferents to phosphoprotein-containing neurons will be determined, using retrograde transport of fluorescent tracers combined with immunocytochemistry. The final phase of this project will involve interrupting these afferents for the purpose of determining their influence on phosphoprotein mRNA expression, both in the adult and developing rat. These studies represent the next stage in defining the role played by phosphoproteins and their presumptive first messenger systems in the central nervous system. Elucidation of the morphological basis for observed biochemical interactions between neurotransmitters and phosphoproteins would appear to be a critical component of the search for integrated mechanisms underlying brain function and dysfunction.